Chapter 8: Force and Laws of Motion

8.1 Balanced and Unbalanced Forces

A force can change the state of motion of an object or change its shape and size. Balanced forces keep an object at rest or uniform motion, while Unbalanced Forces cause acceleration.

8.2 Newton's First Law of Motion

The Law of Inertia

An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.

Inertia: The natural tendency of an object to resist changes in its state of motion. Mass is a measure of inertia.

8.4 Momentum

Momentum (p) is the product of mass (m) and velocity (v).

p = m Ɨ v SI Unit: kg m/s

8.5 Newton's Second Law of Motion

Mathematical Formulation

The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

F = m Ɨ a F: Force (Newton), m: Mass, a: Acceleration

8.6 Newton's Third Law of Motion

Action & Reaction

To every action, there is an equal and opposite reaction and they act on two different bodies.

Example: Reversing of a gun (recoil), a sailor jumping out of a boat.

Key Points

  • 1 Newton (N) = 1 kg m/sĀ².
  • Momentum is a vector quantity with the same direction as velocity.
  • Conservation of momentum: Sum of momenta before collision = Sum after collision.